Growing Tuberous Begonias
By Kim Haworth
We drove down to Capitola recently to take photos of fuchsias. Capitola isn’t too far from the Bay Area and there is plenty to see once you are there. My favorite nursery on the coast is Antonelli Brothers, located on Capitola Road just south of Santa Cruz. Antonelli’s specializes in fuchsias and begonias – I guess that’s why Capitola is the begonia capitol of the world. They have an annual begonia festival in town to celebrate these magnificent tubers.
If you have been growing begonias, you know that now is the time to put them to bed for the year. If you are a begonia novice, here are a few tips for preserving your tubers for next season. Anything of value must be treated with respect, and begonia tubers are no exception. As soon as the lower leaves on the plants begin to yellow, stop watering the plants. You can leave them in the ground at this point if you wish, but I prefer to pull them as soon as they begin to show signs of dormancy. If you forget about them over the winter months, they will rot in the ground and then you will be left with nothing. Dig, not pull, the entire plant from the soil. Shake off as much of the loose soil as possible and lay the plants in a single layer in a dry location away from full sun. I like to turn nursery flats upside down and place the plants on those to allow for maximum air circulation. In about one month, the foliage will be dry and brown. At that point break it gently away from the base of the tuber, shake off any excess soil, then rinse the tubers in fresh water to remove any remaining soil. Place the prepared tubers in a nursery flat lined with dry newspaper, then place them back in the dry location away from the sun until they are pretty much dry to the touch. At this point, discard any tubers that are damaged or showing signs of rot. I like to dust the tubers with sulfur powder to discourage mold and fungus disease during storage. Place the prepared tubers in single layers between pads of newspaper and store in a cool, dry place until planting time in rolls around again in April or May. A bottom shelf in the garage is perfect for storing begonia tubers. Also, please make sure that they are stored in paper, never plastic. Plastic retains moisture and will cause your precious tubers to rot.
Begonia tubers get larger and larger over the years. The resulting plants from those large tubers are going to be magnificent. Eventually single tubers can reach 5 – 7 inches across.
When planting time comes around next spring, check the stored tubers. They should be starting to show signs of life. Little pink nubs will be evident on the concave side. Make sure that you plant them right side up! Prepare the soil in the planting bed after the soil has warmed with plenty of organic matter. I like to grow begonias in containers filled with 100% oak leaf compost, but sometimes that’s hard to find. Any fast draining, rich potting soil will suffice. Lay the tuber with the pink nubs and the concave side facing up. Don’t plant them deeply in the soil please. Just lay the tuber on the surface and gently push it into the soft soil to settle it in place. Water immediately after planting and set the containers in a warm, shady location.
When you begin to see some active growth, begin fertilizing with a high nitrogen fertilizer every two weeks. Begonias don’t need nearly as much water as people believe, so water only when the top two inches of soil feels dry to the touch, and please water only in the morning hours. Begonias, although hardy, are susceptible to powdery mildew.
When the plants begin to set flower buds, switch to 0-10-10 fertilizer and continue fertilizing every two weeks.
I have tremendous success with these plants and this is the regime I follow. I hope you have as much luck with them as I do!